Incidence of hospital-acquired infections has been increasing in recent years at an alarming rate causing great concern among the staffs of these institutions. Many disinfection and sterilization techniques have been employed in an attempt to alleviate this problem. Steam sterilization under pressure has been widely used. However, this method has proven to be impracticable in that it requires expensive equipment and skilled technicians and does not lend itself to the disinfection of objects such as hospital beds, walls, floors or delicate instruments which are sensitive to elevated temperatures.
It has long been the feeling among hospital and medical personnel that a chemical germicide capable of sterilizing materials difficult to sterilize by steam sterilization and stable over relatively long periods of time would be highly desirable. Such a germicide must not only be active against vegetative bacteria but also against fungi, viruses and spores and must have the ability to penetrate tissue and materials, be relatively non-toxic, retain its activity in the presence of organic materials, be non-reactive to rubber and plastics, reach hard-to-get-at places, disinfect quickly, be substantially odorless, be non-corrosive, be non-irritating, be relatively easy to apply, and be safe for use on delicate or sensitive instruments.
Considerable research effort has been expended in finding and developing such a chemical germicide which would provide quick and safe sterilization and substantially replace steam sterilization. Unfortunately all presently known germicidal compositions have been found unacceptable for various reasons. The phenols and formaldehyde compositions which were originally intended to replace steam sterilization have been used and have considerable bactericidal activity, but both have objectionable odors and considerable toxicity. Ethanol, isopropyl alcohol and the quaternary ammonium compounds have been used, and though less odorous and toxic, lack the activity of the phenols and formaldehyde compositions.
Saturated dialdehydes, such as aqueous solutions of glutaraldehyde, have been found to possess surprisingly good disinfectant properties. However, while commercially available glutaraldehyde solutions by themselves having a pH ranging from 2.7 to 3.7 exhibit microcidal properties, they are not sporicidally active.
Compositions comprising saturated dialdehydes with alkalinating agents, such as alkali metal carbonates, bicarbonates or hydroxides and certain secondary and tertiary amines, in solution having a pH ranging from 7.5 to 10 have also been used. Such compositions are more fully described in U.S. Pat. No. 3,016,328. Though such compositions are quite satisfactory as chemical sterilization agents, their stability and potency retention is severely limited thereby rendering them commercially unfeasible except for specialized application. Furthermore, these disinfectant compositions are prepared in solution form preferably containing from 50 to 80% lower alkanol, such as methanol; use of such large amounts of alcohol could have a deleterious solvent effect on equipment.
U.S. Pat. No. 3,282,775 discloses chemical sterilization compositions comprising a saturated dialdehyde containing from 2 to 6 carbon atoms and a cationic surface active agent which may be used in either aqueous or alcoholic solutions. These compositions, as in the case of other prior art disinfectants, rapidly lose their potency once they have been formulated for sterilization use.
It has been found that saturated dialdehydes such as glutaraldehyde can be stored as an acidic aqueous solution (pH 2.5-4.5) at room temperature for 6 to 12 months without significant degradation of the material. However, as indicated hereinbefore, in acidic solution, glutaraldehyde is not sporicidally active. Moreover, near neutral or basic solutions of glutaraldehyde (which are sporicidally active) rapidly lose their potency primarily due to polymerization of the product. Further, elevated temperatures induce polymerization.
Until now the problem of maintaining potency of approximately neutral or basic solutions of glutaraldehyde over long periods of time has remained virtually unresolved. Rather than resolving this problem by developing a neutral or basic glutaraldehyde-containing formulation stable over substantial periods of time, the problem has been sidetracked or avoided by maintaining glutaraldehyde solution as an acidic solution until just prior to use when an alkaline material such as an alkali metal carbonate or certain amines would be added to the acidic solution thereby making it basic. Unfortunately, even this rather "indirect" approach to resolve the stability problem of the basic formulation has rather serious limitations in that the basic formulations apparently lose enough of their potency, due to chemical change, after only 2 to 3 weeks render them virtually ineffective as disinfectants.
It has now been found that stability and potency of saturated dialdehyde based disinfectants can be maintained over relatively long periods of time, substantially longer than prior at compositions, by incorporating in the disinfectant containing saturated dialdehyde, an alkali metal salt of a hydrocarbon carboxylic acid. The alkali metal salt not only acts as a buffer to stabilize pH of solutions of the dialdehyde to within the range of from about 6 to about 8, thereby enhancing disinfectant activity of the dialdehyde, but also inhibits polymerization of the dialdehyde, thereby increasing its stability and shelf-life and maintaining its potency against vegetative bacteria, fungi, viruses and spores over substantially longer periods than was possible with prior art neutral or basic solutions of dialdehyde. Furthermore, it has been found that stability and retention of potency of the dialdehyde is further enhanced by employing with the dialdehyde and alkali metal salt of a hydrocarbon carboxylic acid, an alcohol, diol and/or triol.
In fact, the combination of the alkali metal salt of the hydrocarbon carboxylic acid and the alcohol, diol and/or triol has been found to exhibit synergistic properties in enhancing stability and potency retention properties of basic or approximately neutral dialdehyde-containing formulations.